SystemUI: apply alpha value to all layouts.

Change-Id: I27d5a69eac50053ca34679bf7f6aed821245e132
SystemUI: fix calculating alpha for back button in landscape mode.

Change-Id: Iea7a2eed86d4b65d3772b95f613d1853c66a0158

Conflicts:
	packages/SystemUI/src/com/android/systemui/statusbar/phone/NavigationBarView.java